In the Automatically Switched Optical Network (ASON), for setup of the Label Switched Path (LSP) for a transmission service, it is required to compute by using a path computation algorithm, Constrained Shortest Path First (CSPF), based on topology resources of the current Network. When computing a path, a route computation element is a Routing Controller (RC), which is a route computation element installed within a node, or a Path Computation Element (PCE), which is a route computation element installed external to the node. The route computation element is generally based on the principle of First Come, First Compute, that is, an LSP service which is initiated to be set up first requires to preempt optimal resources of a topology (such as the shortest path, etc.) preferentially.
Therefore, in the current network, when more and more LSP paths are set up, and the setup paths are not released, then available resources of the topology of the network will be gradually reduced, which may ultimately cause that resources (an optical layer or an electrical layer) on some of the paths are exhausted and an available LSP path cannot be computed since resources of the topology have been occupied. In this case, even for a service with a very high level (such as a diamond-level service), when a fault occurs, it cannot ensure restoring rerouting of the service with the very high level is successful, which strongly affects user experience of a service at a high reliability level. As a result, some operators propose an idea of resource preemption, that is, for that restoring scenario, resources of other services are allowed to be preempted. Of course, since preemption will cause interruption of other services, the preemption is mainly used only when the service is restored.
For the abovementioned scenario, currently, G.709 V3 routing standard proposal, draft-ietf-ccamp-gmpls-ospf-g709v3, defines 8 priorities (priority 0 to priority 7, where 0 is the highest priority and 7 is the lowest priority) for each available ODUk timeslot in link resource information of Optical Data Unit k (ODUk) flooded according to the Open Shortest Path First (OSPF) protocol. The format of Bandwidth sub-TLV (Type Length Value) as shown in Table 1 below is as follows:
TABLE 10 12301  2  3  4  5  6  7  8  9 01  2  3  4  5  6  7  8  901  2  3  4  5  6  7  8  901Type = 1 (Unres-fix)LengthSignal type Num of stagesTSTSGResPriorityStage #1. . .Stage #NPaddingUnreserved ODUj at Prio 0. . .Unreserved ODUj at Prio 7Unreserved Padding
Herein, the Unreserved ODUj at Prio 0 to the Unreserved ODUj at Prio 7 represent the numbers of timeslots of idle ODUj at the priority 0 to the priority 7, respectively. In practical application, a Setup Priority and a Hold Priority are designated to each LSP service. The rule is determined that when a service at high “Setup Priority” is being restored and rerouted, if available idle resources are insufficient, resources occupied by other services at low “Hold Priority” may be preempted to ensure that the service at high “Setup Priority” is restored successfully preferentially. For example, as shown in FIG. 1, for the copper-level ODUk switching service 1, of which the “Setup Priority” is 2 and the “Hold Priority” is 1; for the copper-level ODUk switching service 2, of which the “Setup Priority” is 4 and the “Hold Priority” is 3, when the copper-level service 1 breaks down to trigger dynamic rerouting, and there is no idle resources (resources are occupied by the copper-level service 2), since the “Setup Priority” of the copper-level service 1 is higher than the “Hold Priority” of the copper-level service 2, during path computation for restoring the copper-level service 1, the resource occupied by the copper-level service 2 may be preempted to realize successful restoration of the copper-level service 1. After an OSPF protocol stack floods available ODU timeslots on each electrical layer link according to the priorities, the RC or the PCE can select preemptable resources one priority by one priority according to priorities from the lowest priority to the highest priority during the route computation, based on the abovementioned method, thus completing the path computation.
At present, what is proposed in the current standard is limited to priority extension of the available timeslots of an ODUk link, that is, what is proposed in the current standard only solves the preemption when the ODUk link has no idle resources. This method can only solve the problem of priority preemption for restoring an electrical layer service. But with respect to priority preemption for restoring an optical layer service, there is no solution.